In recent years, magnetic resonance (“MR”) diagnostic devices, which are also referred to below as MR devices (e.g., magnetic resonance tomograph=MRT), have become particularly significant due to their examination methodology, which is gentle on the patient, non-invasive, and entirely pain-free and without side effects. Typical medical implants comprised of conductive materials, which also include electrophysiological catheters and/or known intracardial electrodes implanted temporarily or permanently for intervention purposes, have the problem that they heat up considerably in magnetic resonance diagnostic devices under the influence of the electromagnetic radiation generated thereby, and also due to the emission of the induced energy in the region of their contact surface(s) with tissue, i.e., electrode poles which are designed as ring electrodes and tip electrodes. The reason therefore, in particular, is the solid metallic supply leads to the contact surfaces, which function as antennas; due to the insulation thereof, the antenna currents induced by high-frequency (“HF”) fields are diverted into the body electrolytes only at the contact surfaces that form the electrical boundary surface with the tissue. The aforementioned HF fields function in a working frequency range, for instance, of 21 MHz in the case of a 0.5 tesla MR tomograph. According to the current state of the art, the working frequency range can reach up to 300 MHz for a 7 tesla MR tomograph, and is typically 64 MHz for a 1.5 tesla MR tomograph. Since the tissue in the vicinity of the electrode pole(s) can become heated to an extreme extent, minimally invasive catheter ablations cannot be performed using magnetic resonance imaging.
To prevent or minimize the dangerous heating of the body cells, the maximum antenna current must be limited or reduced. Known solutions primarily in the field of intracardial electrode leads provide discrete components which function as band-stop filters or low-pass filters and, thereby, limit the lead resistance of the antenna for the frequencies of interest. Other known solutions provide capacitors which are connected in parallel to the insulation and, thereby, dissipate the antenna current.
Example documents in this regard are U.S. Pat. No. 6,944,489, U.S. Publication No. 2003/0144720, U.S. Publication No. 2003/0144721, and U.S. Publication No. 2005/0288751 (and the parallel documents U.S. Publication No. 2005/0288752, U.S. Publication No. 2005/0288754, and U.S. Publication No. 2005/0288756, which comprise substantially identical wording and were published in parallel).
Basically, it is possible to influence the inductance and capacitive coupling of the antenna using design measures, and to thereby reduce the flow of antenna current, dissipate the same, or shift the resonant frequency. The design requirements on a medical instrument of the initially described type, which are important in terms of therapy, typically permit very little leeway in this regard, however.
Furthermore, in contrast to the highly simplified consideration examined herein, antennas also have further resonant frequencies, and so shifting the resonant behavior of the electrode may fulfill the resonant condition of an MR device having other HF frequencies. This approach is therefore not advantageous.
Document EP 0 884 024, which is also referenced as technological background, discloses the case of which a capacitor is connected between the supply leads for the ablation pole of a catheter and a measurement pole which is also disposed thereon and is used to receive EKG signals. Due to the capacitor, high-frequency energy can be delivered via the ablation electrode to perform ablation, and an EKG signal can be received at the same time.
The disclosed dissipation device and system are directed at overcoming one or more of the above-identified problems.